Nonexponential decay of autoionizing shock wave packets

Femtosecond laser pulses have been used to promote calcium atoms in station ary 4snd Rydberg levels to superpositions of 4pnd autoionizing states. The rapid excitation of the 4s core electron generates a "shock wave packet" th at propagates through the previously stationary Rydberg wave function. The nonexponential decay of the autoionizing wave packet is probed using a seco nd isolated-core excitation from the 4pnd to the 4dnd autoionizing series. Our measurements are in good agreement with the predictions of rime-depende nt multichannel quantum defect theory.